Campbell Scientific 253-L and 257-L (Watermark 200) Soil Matric Potential Sensors - Manual (Page 33)

253-L and 257-L Soil Matric Potential Sensors
;Output hourly data
20: If time is (P92)
1: 0
Minutes (Seconds --) into a
2: 60 Interval (same units as above)
3: 10 Set Output Flag High (Flag 0)
21: Set Active Storage Area (P80)
1: 1
Final Storage Area 1
2: 60 Array ID
22: Real Time (P77)
1: 1220
Year,Day,Hour/Minute (midnight = 2400)
23: Average (P71)
1: 5
Reps
2: 1 Loc [ T107_C_1 ]
24: Sample (P70)
1: 10
Reps
2: 6 Loc [ WP_kPa_1 ]
7.4 Interpreting Results
As a general guide, 253 and 257 measurements indicate soil matric potential as
follows:
0 to –10 kPa = Saturated soil
–10 to –20 kPa = Soil is adequately wet (except coarse sands, which are
beginning to lose water).
–20 to –60 kPa = Usual range for irrigation (except heavy clay).
–60 to –100 kPa = Usual range for irrigation for heavy clay soils.
–100 to –200 kPa = Soil is becoming dangerously dry for maximum
production.
8. Troubleshooting
To test the sensor, submerge it in water. Measurements should be from
–3 to +3 kPa. Let the sensor dry for 30 to 48 hours. You should see the
reading increase from 0 to 15,000+ kPa. If the reading does not increase to
15,000 kPA, replace the sensor. If the reading increases as expected, put the
sensor back in the water. The reading should run right back down to zero in 1
to 2 minutes. If the sensor passes these tests but it is still not functioning
properly, consider the following:
1. Sensor may not have a snug fit in the soil. This usually happens when an
oversized access hole has been used and the backfilling of the area around
the sensor is not complete.
2. Sensor is not in an active portion of the root system, or the irrigation is not
reaching the sensor area. This can happen if the sensor is sitting on top of
a rock or below a hard pan which may impede water movement. Re-
installing the sensor usually solves this problem.
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